A nanocomposite of graphene/MnO2 nanoplatelets was prepared by one-step chemistry route at room temperature. The microstructure was characterized by X-ray diffraction, N-2 absorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Both TEM and SEM images show that MnO2 nanoplatelets are homogeneously distributed on the graphene nanosheets. The electrochemical properties were tested by cyclic voltammetry, galvanostatic charge-discharge experiments. The nanocomposite exhibited high lithium capacity (905 mAh g(-1) at 100 mA g(-1)). The superior lithium storage capability can be attributed to the "open" structure: the large effective surface area and short diffusion paths.